The present invention relates to an improvement in the field of testing oil well streams and more particularly, but not by way of limitation, to a novel method and automated system for determining the phase fractions of gas, oil, and water and oil-emulsion of an oil well stream.
It is well known that in the majority of oil wells, the fluid flowing or being pumped from an oil well is not pure oil but is a mixture of gas, oil water, gas, chemicals and at times solids. While the gas, oil, and water do occur in a free state quite often these items often flow in an emulsion condition. It is also well known that it is important to monitor the production or flow of a particular oil well or a plurality of oil wells in a particular field or region. The net oil production from a well must be determined as well as the volume of oil, gas, and water that are present in the well stream.
The oldest and most widely accepted method of testing oil well production fluids was the three phase separator tank arrangement which consisted primarily of a large receiving tank into which a predetermined well stream flowing from an oil well would be deposited and allowed to stand. The effect of gravity on the sample would cause the free water to settle to the bottom of the tank, the oil to rise to the top of the settled water, and the gas to rise above the oil. This arrangement was commonly referred to as a three phase separator. The gas is allowed to escape from the tank and the remaining volummes of water and crude oil are measured. The crude oil was tested to determine its water content or wetness by a capacitance probe. Other factors of the test sample were also measured and a fair estimate of the net oil being produced was made.
The three phase separator was prone to a number of shortcomings. Such an apparatus was large and cumbersome and required the exercise of care by skilled technicians in its operation. The time required for the emulsions, oil, water, and gas of a well stream to separate adequately often required many hours or days. Also, the capacitance probes employed were extremely sensitive to certain external factors and were not dependable. The end result was that the method yielded the net oil of a production on about 75% of wells tested with a margin of error of about 10%.
More recently, U.S. Pat. No. 3,911,256 presented an improved apparatus for testing and analyzing a well stream. This patent provided for diverting a predetermined volummetric portion of the flow of a well stream and then measuring the pressure of the isolated portion. This portion was then subjected to compression of the gas fraction so that the volume of gas could be mathematically determined. Other measurements were made of the test portion so that the volume of gas and proportions of each liquid in the well stream test portion could be determined by mathematical comparative calculations.
U.S. Pat. No. 4,852,395 discloses a three phase fluid flow measuring system for measuring the volummetric fractions of gas, water and oil which included a centrifugal separator for conducting primary separation of gas from the liquid phase. A sample of the resultant fluid stream was conducted to a test chamber where it was subjected to an increased pressure. The transmissivity of microwave energy through the test sample was then measured as a way of determining the gas phase in the liquid phase and to determine the volummetric fraction of water and oil in the liquid phase.
It is also known in the art to segregate a test sample of a well stream and to record the flow rate, temperature, pressure, and weight of such sample and to also determine the aggregate capacitance of the sample. The net oil, gas, and water content are then determined mathematically, after corrections for temperature.
However, all known prior art systems and methods are subject to a number of shortcomings. Some systems will not provide accurate liquid flow data if the well stream produces over a 5% gas fraction or if the fluids do not separate into oil and water fractions by the force of gravity within a five minute period. Also, inaccurate data is obtained as the degree of emulsion of the fluids increases or varies.
In addition, the prior art systems are temperature dependant. As the test chamber or test probes are fouled by oil build up, test readings begin to vary unacceptably. Great difficulties have been experienced in calibrating capacitance probes which require a cumbersome difficult procedure. Also, recalibration of current systems must be made in the event that the capacitance of the oil or water changes over time, or with the addition of chemicals into the well stream. However, the biggest problem remains with emulsions that remain after the time permitted for separation of the fractions and the inconsistencies in capacitance readings that result in indicating a larger water content than is actually present.
While the prior patents and prior art commercial devices have been successful to a certain extent, it is nonetheless clear that substantial room exists for affecting an advance in the art which overcomes these shortcomings in a practical and efficient manner.
It is a general object of the invention to provide an improved method and system for testing and analyzing oil production fluid to determine the net oil content thereof and which overcomes many of the shortcomings that are found in the methods and apparatus of the known prior art.
Another object of the invention is to provide an improved method and automated system for determining the phase fractions of an oil well stream wherein the gas, water, and oil fractions of a test sample of the well stream are not separated nor need to be separated in the process of analyzing and calculating the new oil content.
Yet another object of the invention is to provide a method and system which may accurately test and analyze test well samples which have gas fractions from 0 to 100% of the total well production volume.
Another object of the invention is to provide and improved method and system for analyzing a production well stream which will reduce or substantially minimize the effects of any accumulated oil coating on the interior of the test chamber.
It is a further object of the invention to provide a method of analyzing a test sample of a production well stream which will provide additional data beyond the phase fractions of gas, oil and water and which will minimize the dependency on entry of accurate data relating to the densities of oil, gas and water, permitivity of oil, water, gas, etc. thereby providing "live" oil and water density data.
Also, it is an object of the improved method to permit analysis and quantification of the degree of oil-water emulsion of the test sample of the well stream and to indicate the separation rate of the oil and gas fractions.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.